Catalysts containing activated titanium compounds supported by magnesium halides are hitherto known as those for use in the preparation of homopolymer of ethylene or .alpha.-olefin, or olefin polymers such as an ethylene/.alpha.-olefin copolymers.
The olefin polymerization catalysts as referred to above (hereinafter they are sometimes used, including also copolymerization catalysts) are known to include such catalysts as comprising a solid titanium catalyst component containing magnesium, titanium, halogen and an electron donor, and an organometallic compound catalyst component.
The catalysts mentioned above have high activities in polymerization or copolymerization of .alpha.-olefin such as propylene or butene-1 (hereinafter the term polymerization is sometimes used, including also copolymerization) as well as In polymerization of ethylene. In addition thereto, the polymers or copolymers obtained by the use of these catalysts are high in stereospecificity.
Of the catalysts as mentioned above, those comprising in particular a solid titanium catalyst component having supported thereon an electron donor selected from carboxylic esters, a typical example of which is phthalic ester, an aluminum-alkyl compound as a co-catalyst and a silicon compound having at least one Si-OR linkage (wherein R is a hydrocarbon radical) exhibit excellent performance when they are used in the above-mentioned polymerization or copolymerization.
The present inventors conducted researches with the view of obtaining olefin polymerization catalysts excellent by far in polymerization activity and stereospecificity, and have eventually accomplished the present invention on the basis of their finding that an object of the invention can be best attained by using a catalyst comprising a solid titanium catalyst component containing magnesium, halogen, titanium and a compound having two or more ether linkages with a plurality of intermediately existing bonding atoms, or a catalyst comprising a solid titanium catalyst component containing magnesium, titanium, halogen and an electron donor, an organometallic compound and the above-mentioned compound having two or more ether linkages.
In this connection, it has been found that polymers low in stereospecificity are obtained by the use of a catalyst system comprising a solid catalyst component obtained by contact of a solid component containing magnesium, titanium, halogen atom and an electron donor with an alkoxy-containing aromatic compound having 1-6 alkoxy groups substituted in the benzene ring, in combination with an organoaluminum compound (Japanese Patent L-O-P Publn. No. 236203/1989).